Zhou, Zhiyan , Quan, Cheng , Liu, Yusheng .
Tertiary Ginkgo ovulate organs with associated leaves from North Dakota, USA and its evolutionary significance.
The evolutionary history of Ginkgo, a living fossil once flourished in the geological time, has been better understood for the Mesozoic Era, but was still elusive in the Tertiary because of the rarity of reproductive organs. We here describe a new species, Ginkgo cranii sp. nov., based on studies using SEM and LM on well-preserved ovulate organs and associated leaves from the Upper Paleocene Sentinel Butte Formation of North Dakota, USA. The ovulate organ is of the modern type and pedicel-absent, with two ovules seated in separate collars directly attached to the peduncle, but only one of them is matured. The fully developed ovules are platyspermic, 12-14 mm long by 11-14 mm wide and about 10-12 mm thick. Stomata with deeply-sunken guard cells and slightly-raised subsidiary cells are sparsely distributed among epidermal cells which are characterized by dome-like, strongly bulging periclinal walls and developed anticlinal wall flanges in integument and collar cuticles. The pollen grain adhered to the cuticle is fusiform with a narrow medium colpus and finely granulate exine. The associated leaves are generally similar to the ovulate organ in cuticular structure, especially in having epidermal cells with more or less bulging periclinal walls and developed periclinal wall flanges. Ginkgo cranii is the only Tertiary species of the genus described so far, of which the ovulate organs are known. The study further corroborates the hypothesis that modern Ginkgo was evolved from its ancestors by reduction, and is helpful to classify Cenozoic ginkgos in a natural system.
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1 - Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sci, Nanjing, 210008 , China
2 - East Tennessee State University, Department Of Biology, PO Box 70703, Johnson City, TN, 37614-1710, USA
reduced evolutionary trends
Sentinel Butte Formation.
Presentation Type: Poster:Posters for Sections
Location: Khorassan Ballroom/Chase Park Plaza
Date: Monday, July 11th, 2011
Time: 5:30 PM